Luke 3:7-9, 15-18 (NASB)
7 So he began saying to the crowds who were going out to be baptized by him, “You brood of vipers, who warned you to flee from the wrath to come? 8 Therefore bear fruits in keeping with repentance, and do not begin to say to yourselves, ‘We have Abraham for our father,’ for I say to you that from these stones God is able to raise up children to Abraham. 9 Indeed the axe is already laid at the root of the trees; so every tree that does not bear good fruit is cut down and thrown into the fire.”
15 Now while the people were in a state of expectation and all were wondering in their hearts about John, as to whether he was the Christ, 16 John answered and said to them all, “As for me, I baptize you with water; but One is coming who is mightier than I, and I am not fit to untie the thong of His sandals; He will baptize you with the Holy Spirit and fire. 17 His winnowing fork is in His hand to thoroughly clear His threshing floor, and to gather the wheat into His barn; but He will burn up the chaff with unquenchable fire.”
18 So with many other exhortations he preached the gospel to the people.